Complementation of the PRF-KO phenotype of primary mouse CTLs. Primary mouse CTLs were generated, activated, transfected to express hPRF-WT or hPRF-A91V perforin, sorted, and tested in cytotoxicity assay against SIINFEKL-pulsed EL-4 target cells as described in “Materials and methods.” (A) Data in the larger graph represent the mean ± SE of 4 to 6 independent experiments, and 2 typical Western immunoblots are shown. Each independent experiment was standardized with respect to the level of ⁵¹Cr release induced by hPRF-WT-transfected cells in 20:1 E/T ratio (100%). Activated CTLs from BL/6 mice were used as control. The smaller graph shows the outcome of one typical experiment (mean ± SD of triplicate data points; raw data are shown). The effect of antigen presentation was tested by treating ⁵¹Cr-labeled EL-4 target cells with various concentrations of SIINFEKL peptide. The effector cells were used in 15:1 E/T ratio. (B) Data from a representative experiment are shown as mean ± SD. Inset shows standardized data from a large graph, where the level of specific ⁵¹Cr release from EL-4 targets treated with 10 ng/mL peptide was regarded as 100%.